Single-Channel Safety Output

ABSTRACT

A safety switching device for fail-safely switching on and off an electrical load, and to a system comprising at least two safety switching devices which interact in a fail-safe manner via a single-channel. The safety switching device comprises a fail-safe control unit, a first and a second electronic switching element connected with a first and a second output terminal; and at least one input terminal for receiving a first switching signal that causes a switching of said switching elements. Said first and second switching elements each comprise an output which provides depending on the first switching signal an output signal having a first or second potential. A third output terminal connects said safety switching device to a second safety switching device, providing a clocked signal depending on the first switching signal and being monitored by said control unit for performing a cross fault detection.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of, and claims priority to, currentlypending U.S. patent application Ser. No. 14/259,838 filed on Apr. 23,2014 titled “Single-Channel Safety Output” which is a continuation ofU.S. Pat. No. 8,736,118 filed on Apr. 11, 2011 titled “Single-ChannelSafety Output” and which claims priority to European Patent ApplicationNo EP10161647.2 filed on Apr. 30, 2010. The disclosures of all of whichare expressly incorporated herein.

BACKGROUND

The present invention relates to a safety switching device forfail-safely switching on and off an electrical load. The presentinvention in particular relates to a safety switching device comprisinga fail-safe control unit, a first and second electronic switchingelement, a first and second output terminal and at least one inputterminal for receiving a switching signal that causes switching off saidswitching elements.

The invention further relates to a safety switching device systemcomprising at least two safety switching devices which interact in afail-safe manner.

Safety switching devices are, for instance used in industrial productionenvironments in order to reliably and safely disconnect machines, suchas a hydraulic press or a milling machine, if this is necessary for thesafety of personnel or machinery. Safety switching devices typicallyhave one or more input terminals to which input devices such asemergency stop buttons, two-hand operator buttons, guard door switchesor light curtains can be connected. An evaluation and control unitevaluates the input signal from these input devices in a fail-safemanner and produces a switching signal on an output side being afunction of same. The evaluation and control unit is also designed tooperate in a fail-safe manner, for instance by providing redundancy. Theswitching signal controls actuators, in particular contactors fordisconnecting the machine from a power supply.

The term “fail-safe” signifies that disconnecting the machine must beensured under all circumstances, even if a functional fault occurswithin the chain comprising the input device, the safety switchingdevice and the actuator. Safety switching devices must therefore bedesigned such that they ensure that the machine being. monitored isalways in a safe state, even in the event of the failure of onecomponent, in the case of broken cables or other malfunctions.Accordingly, the term “safety-switching device” in this context refersonly to those devices and appliances which comply at least with category3 of European standard EN 954-1, or comparable requirements.

In DE 100 11 211 61, a safety switching device and a system of more thanone safety switching device is shown, wherein the safety switchingdevice system comprises two safety switching devices which are connectedto each other via two lines. By providing two signals which are clockedin a way that they have different signals, a cross connection betweenthose two lines can be detected by means of an additional feedbacksignal. With this configuration, a category 4 safety level can beachieved.

This known solution, however, suffers from the drawback that in order tobe able to classify the system as safety category 4, an enhancedexpenditure in terminals and additional lines has to be provided.

There is therefore a need to provide a safety switching device and asystem of safety switching devices which allow for a cross-faultdetection on the one hand and can be realized in a particularly simpleand economic way on the other hand.

SUMMARY OF THE INVENTION

The present invention provides a safety switching device that overcomesone or more of the drawbacks above. One aspect of the present inventionprovides a single-channel connection between a first safety switchingdevice and a second safety switching device which transmits definedclocked pulses and by monitoring this signal by the first switchingdevice ensures fail safety not via the redundancy of two parallel lines,but via a monitoring of the signal.

According to another aspect of the present invention, the safetyswitching device comprises a third output terminal for connecting thefirst safety switching device to a second safety switching device, thethird output terminal providing a clocked signal depending on the firstswitching signal and being monitored by the control unit for performingthe required cross fault detection. A short-circuiting between the twocoupling lines cannot occur because only one line is provided and thefault connection to 24 V, 0 V, or other differently clocked lines can bedetected.

According to another advantageous embodiment of the present invention,the signal which is output by the third output terminal is suitable forpowering the second safety switching device. This can for instance beachieved by providing an energy storage unit within the second safetyswitching device, such as a capacitor, which transforms the clockedpulse train of the output signal from the first safety switching deviceinto a constant DC power supply, for instance of 5 V.

According to another aspect of the present invention, the clocked signalcomprises a train of defined pulses in the case that the safetyswitching device has a valid safety function. In a preferred aspect,this pulse train has the structure of a predetermined code that can beread by the first and/or the second safety switching device. In the casethat the safety status indicates a fault, the safety switching deviceoutputs at the third output terminal a constant 0 V signal.

According to another aspect of the invention, the first safety switchingdevice monitors the output signal and in case of any cross faults,detects the absence of the correct predetermined code signal.Preferably, the second safety device can first monitor the input signaland also recognizes if the expected code signal is not received. Thepulsed output signal from the third output terminal is fed into a powersupply terminal of the second safety switching device. In the case thatthe 0 V signal is sent to the second safety switching device, no powersupply can be generated from this signal. The second safety switchingdevice either returns to or remains in a safe status.

By using a pulse code for the clocked signal which differs from allother clocked signals present in the safety switching device and thesafety switching device system, according to the present invention across fault to other clocked signals can also be detected. In order toachieve redundancy and therefore comply with a high safety standard, thefailsafe control unit of the safety switching device may comprise tworedundant microprocessors which are operable to monitor the clockedsingle-channel output signal in a parallel way.

To the accomplishment of the foregoing and related ends, certainillustrative aspects of the disclosed innovation are described herein inconnection with the following description and the annexed drawings.These aspects are indicative, however, of but a few of the various waysin which the principles disclosed herein can be employed as is intendedto include all such aspects and their equivalents. Other advantages andnovel features will become apparent from the following detaileddescription when considered in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of a safety switching device systemaccording to the present invention;

FIG. 2 shows an example of a pulse code to be transmitted on thefail-safe single-channel connection; and

FIG. 3 shows a block diagram of a second safety switching device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The innovation is now described with reference to the drawings, whereinlike reference numerals are used to refer to like elements throughout.In the following description, for purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding thereof. It may be evident, however, that the innovationcan be practiced without these specific details. In other instances,well known structures and devices are shown in block diagram form inorder to facilitate a description thereof.

As used in this application, the terms “component”, “system”,“equipment”, “interface”, “network” and/or the like are intended torefer to a computer related entity, either hardware a combination ofhardware and software, software or software in execution. For example, acomponent can be but is not limited to being, a process running on aprocessor, or a processor, a hard disk drive, multiple storage drives(of optical and/or magnetic storage medium), an object, an executable, athread of execution, a program and/or a computer, an industrialcontroller, a relay, a sensor and/or a variable frequency drive. By wayof illustration, both an application running on a server and a servercan be a component. One or more components can reside within a processand/or thread of execution, and a component can be localized on onecomputer and/or distributed between two or more computers.

In addition to the foregoing, it should be appreciated that the claimedsubject matter can be implemented as a method, apparatus, or article ofmanufacture using typical programming and/or engineering techniques toproduce software, firmware, hardware, or any suitable combinationthereof to control a computing device, such as a variable frequencydrive and controller to implement the disclosed subject matter. The term“article of manufacture” as used herein is intended to encompass acomputer program accessible from any suitable computer-readable device,media, or a carrier generated by such media/device. For example,computer readable media can include but are not limited to magneticstorage devices (e.g., hard disk, floppy disk, magnetic strips . . . ),optical disks (e.g., compact disk (CD), digital versatile disk (DVD) . .. ), smart cards, and flash memory devices (e.g., card, stick, key drive. . . ). Additionally it should be appreciated that a carrier wavegenerated by a transmitter can be employed to carry computer-readableelectronic data such as those used in transmitting and receivingelectronic mail or in accessing a network such as the Internet or alocal area network (LAN). Of course, those skilled in the art willrecognize many modifications may be made to this configuration withoutdeparting from the scope or spirit of the claimed subject matter.

Moreover, the word “exemplary” is used herein to mean serving as anexample, instance, or illustration. Any aspect or design describedherein as “exemplary” is not necessarily to be construed as preferred oradvantageous over other aspects or designs. Rather, use of the wordexemplary is intended to present concepts in a concrete fashion. As usedin this application, the term “or” is intended to mean an inclusive “or”rather than an exclusive “or”. That is unless specified otherwise, orclear from context, “X employs A or B” is intended to mean any of thenatural inclusive permutations. That is if X employs A; X employs B; orX employs both A and B, then “X employs A or B” is satisfied under anyof the foregoing instances. in addition, the articles “a” and “an” asused in this application and the appended claims should generally beconstrued to mean “one or more” unless specified otherwise or clear fromcontext to be directed to a singular form.

Furthermore, the terms to “infer” or “inference”, as used herein, refergenerally to the process of reasoning about or inferring states of thesystem, environment, and/or user from a set of observations as capturedvia events and/or data. Inference can be employed to identify a specificcontext or action, or can generate a probability distribution overstates, for example. The inference can be probabilistic, that is, thecomputation of a probability distribution over states of interest basedon a consideration of data and events. Inference can also refer totechniques employed for composing higher-level events from a set ofevents and/or data. Such inference results in the construction of newevents or actions from a set of observed events and/or stored event datawhether or not the events are correlated in close temporal proximity,and whether the events and data come from one or several event and datasources.

Referring now to the drawings, FIG. 1 schematically shows a safetyswitching device system 100 according to a first embodiment in the mostbasic construction. The system comprises a first safety switching device102 and a second safety switching device 104.

The first switching device 102 may for instance be an emergency stopdevice having safe semiconductor outputs at the terminals 14 and 24. Inorder to allow for an enhanced number of actuating outputs, for instancein the case that several machines or machine elements have to beswitched off in the case of an emergency, there may be the requirementof adding to the first safety switching device 102 either an additionalsafety switching device of the same kind or a contact expansion unitrepresenting a second safety switching device 104.

These contact expansion units 104 supply additional output current pathsas this is generally known, but do not posses logic units of their ownfor processing the signals apart from a logic for monitoring theintegrity of the signals.

Conventional systems, such as the one shown in DE 100 11 211 B4, use twoseparate connections in order to comply with the highest safetystandard, category 4, as IL3. The disadvantage of such a dual channelsolution can firstly be seen in the fact that an additional line and anadditional terminal has to be provided, and that secondly cross faultsbetween these two lines can occur.

According to the present invention, the safety switching device 102comprises a fail-safe single-channel output L11. This single-channeloutput L11 can be connected via a connection line 106 to an input A1 ofthe contact expansion device 104.

The required safety is ensured by transmitting a pulsed output signal onthe single-channel line 106 which can be monitored internally by thesafety switching device 102. By monitoring the power strain of theclocked signal on line 106, short circuits to 24 V and 0 V potential andconnections to lines which have a differently clocked signal can bedetected. Consequently, an essential requirement for fulfilling thestandard category 4 can be met.

The contact expansion device 104 which is connected to the fail-safeoutput L11, receives electric power from the safety output L11 and atthe same time, the status of the safety function.

Although in FIG. 1 only two safety switching devices 102, 104 are shown,it is clear for a person skilled in the art that an arbitrary number ofdevices can be connected via the inventive single-channel output.

FIG. 2 shows an example of the signal 108 that is output by theinventive single-channel safety output terminal L11. The signal 108 mayfor instance be equal to a constant 0 V signal in the case that thesafety function is “not true”, that is indicates the occurrence of afault condition.

On the other hand, if the safety output is “true”, the signal 108 has awell-defined pulse pattern as shown in FIG. 2. This pulse pattern whichrepresents a code can be recognized by an internal monitoring unit (notshown in the figures) of the first safety switching device 102. As thisis usually done by conventional devices, this monitoring is done in atwo-channel manner by two independent microprocessors.

The contact expansion device 104, on the other hand, receives the signal108 and processes same as will be shown with reference to FIG. 3. As canbe derived from this circuit diagram, the second safety switching devicewhich receives the signal at terminal A1 splits the received signal andfirstly, uses it for feeding a power storage capacitor CS and secondly,inputs the signal into the microcontrollers μC1 and μC2.

A DC/DC converter 110 which is connected to the storage capacitor CSgenerates a supply power having a supply voltage of 5 V from the input24 V pulse train signal.

The input A2 of the second safety switching device 102 receives the 0 Vground potential which is also input into the first switching device102.

As soon as the safety function of the first safety switching device 102is “true”, the clocked output L11 produces a clocked signal 108.Consequently, connected second switching device 104 is provided with thesupply voltage via the diode D1, the storing capacitor CS and thevoltage controller 110, representing the necessary operating voltage.The capacitor CS may for instance be an electrolyte capacitor. Any otherstoring means may of course also be used here. When powered by theoutput of the DC-DC converter 110, the microcontrollers μC1 and μC2start up. If these microprocessors now additionally detect a valid pulsecode at their I/O terminals, the driver units 112, 114 are controlled totrigger the relays 116 and 118 for providing a switched-on status of thesafety outputs 14 and 24.

Consequently, A1 must receive a voltage different from 0 V whichadditionally must have a valid pulse pattern in order to cause thesafety switching device 104 to output a valid output signal. With theinventive safety device topology, it is possible to fulfill therequirements of category 4 of the safety standards, although only asingle-channel connection is employed.

This high safety category is achieved on the side of the second safetyswitching device due to the predetermined dynamics of the signal and thetwo-channel evaluation of this signal by using both microprocessors. Onthe other hand, the high safety standard on the side of the sendingfirst safety switching device 102 is achieved by means of a two channelfeedback of the output signal generated at terminal L11 whereby shortcircuiting to 24 V, 0 V, or to other clocked signals can be detected.

Furthermore, by feeding back this output signal to both processors in aparallel way, a plausibility check can be performed in order to monitorthe fault free function of the microprocessors.

However, in case of a fault condition, the first safety switching device102 outputs a constant 0 V signal at terminal L11 because the safetyfunction of this device is no longer “true”. Then also the safetyoutputs of the subsequent safety switching device 104 are switched offbecause, firstly, no valid clocked signal pattern is supplied to inputterminal A1 and secondly, because the input terminal A1 no longerreceives a supply voltage which could supply energy to themicroprocessors and the relays. As can be seen in FIG. 3, the relays116, 118 can also be powered by the output from the DC/DC converter 110.

Of course, the single-channel safety output according to the presentinvention can also be used for connecting to any other safety input ofdifferent safety switching devices. The system is particularly suitablefor connecting a safety switching device with one or more a delayedexpansion modules.

The invention claimed is:
 1. A safety switching device systemcomprising: a contact expansion unit that includes a first input; thecontact expansion unit including a power storage device, a firstmicrocontroller, and a second microcontroller that are each connected tothe first input and a power converter that is connected to the powerstorage device and configured to generate a supply power associated withstart-up of the first microcontroller and the second microcontroller;and the contact expansion unit including a first output and a secondoutput that are each configured to communicate a signal from the contactexpansion unit when a valid pulse code is detected at each of the firstmicrocontroller and the second controller.
 2. The safety switchingdevice system of claim 1 further comprising a first safety switchingdevice configured to communicate a signal to the first input of thecontact expansion unit.
 3. The safety switching device system of claim 2wherein each of the contact expansion unit and the first safetyswitching device each include a second input that are connected to oneanother.
 4. The safety switching device system of claim 2 wherein thevalid pulse code is derived from an operating condition of the firstsafety switching device.
 5. The safety switching device system of claim4 wherein the valid pulse code is a clocked signal derived from thefirst safety switching device that is communicated to each of the firstmicrocontroller and the second microcontroller of the contact expansionunit.
 6. The safety switching device system of claim 1 furthercomprising a respective driver and a respective relay disposed betweeneach of the first output and the first microprocessor and the secondoutput and the second microprocessor of the contact expansion unit. 7.The safety switching device system of claim 1 wherein the powerconverter is further defined as a DC/DC converter.
 8. A safety switchingdevice arrangement comprising: a first safety switching deviceconfigured to generate an output signal; a contact expansion unit havingan input configured to receive the output signal from the first safetyswitching device, the contact expansion device including a power storagedevice, a first microcontroller, and a second microcontroller that areeach configured to receive a signal from the input and initiateoperation of the first microcontroller and the second microcontrollerfrom a signal that is acquired from the power storage device and enableoperation of a first output and a second output of the contact expansionunit when the output signal from the first safety switching device isprovided as a valid pulse code.
 9. The safety switching devicearrangement of claim 8 further comprising a relay disposed between eachof the first output and the second output of the contact expansion unitwhose operation is controlled by at least one of the firstmicrocontroller and the second microcontroller of the contact expansionunit.
 10. The safety switching device arrangement of claim 8 wherein thefirst safety switching device further comprises a first microcontroller,a second microcontroller, and a plurality of outputs wherein one of theplurality of outputs is connected to the input of the contact expansionunit.
 11. The safety switching device arrangement of claim 10 furthercomprising a second safety switching device.
 12. The safety switchingdevice arrangement of claim 11 wherein each of the first safetyswitching device, the second safety switching device, and the contactexpansion unit each include an input that are electrically connected toone another.
 13. The safety switching device arrangement of claim 8further comprising a power converter disposed between the power storagedevice and a respective input associated with each of the firstmicrocontroller and the second microcontroller.
 14. A method ofconfiguring a safety switching arrangement, the method comprising:connecting a first input of a contact expansion device to an output of asafety switching device; communicating a signal received at the firstinput to each of a power storage device, a first microcontroller, and asecond microcontroller; communicating a signal from the power storagedevice to generate a start-up signal associated with operation of eachof the first microcontroller and the second microcontroller; andenabling operation of at least one of a first output and a second outputof the contact expansion device when a valid pulse code is received at arespective input/output terminal associated with the firstmicrocontroller and the second microcontroller.
 15. The method of claim14 further comprising connecting a second input of the contact expansiondevice to an input associated with the safety switching device.
 16. Themethod of claim 15 further comprising connecting an input of anothersafety switching device to the second input.
 17. The method of claim 14further comprising converting the signal from the power storage deviceduring communication of the signal from the power storage device togenerate the start-up signal associated with operation of each of thefirst microcontroller and the second microcontroller.
 18. The method ofclaim 14 further comprising manipulating a condition of a relayassociated with each of the first output and the second output when thevalid pulse code is received.
 19. The method of claim 14 wherein thevalid pulse code is generated by the safety switching device as aclocked signal.
 20. The method of claim 14 further comprising performinga cross fault detection associated with operation of at least one of thecontact expansion device and the safety switching device.